Stepped supports between glass plate display screen and cathode ray tube faceplate

ABSTRACT

A planar member such as a phosphor coated fiber optic plate, having a thermal coefficient of expansion that is incompatible with that of a cathode ray tube envelope and faceplate, is accurately supported a precise distance from the inner surface of the faceplate by a plurality of step-shaped supports having a spacer portion disposed between the planar member and faceplate and a shoulder portion adjacent to the periphery of the planar member. Conductive spring clip means affixed to the supports apply a retaining force to the planar member and make electrical contact thereto.

United States Patent 1 [111 3,732,45 1

Steinberg et al. May 8, 1973 54 STEPPED SUPPORTS BETWEEN GLASS 3,502,942 3/1970 Khan et al. ..313/85 s PLATE DISPL Y SC N AND 3,507,551 4 1970 Stetten ..313 92 LF CATHODE RAY TUBE FACEPLATE 3,543,072 11/1970 McNeill ..313/85 S [75] Inventors: David R. Steinberg; William T. Sutton, both of Raleigh, NC.

[73] Assignee: Corning Glass Works, Corning,

[22] Filed: Nov. 16, 1970 [21] Appl. No.: 89,716

[52] US. Cl ..313/91, 313/92 [51] Int. Cl ..H01j 29/12, l-lOlj 29/02, H01j29/18 [58] Field of Search ..313/92 LP, 92 PD, 313/85 S, 65 LP, 65 T [56] References Cited UNITED STATES PATENTS 2,941,030 6/1960 Birch-Field ..3l3/92 R X 3,400,214 9/1968 Hamann ..350/l60 P 3,519,742 7/1970 Bjelland ....350/160 P X 2,856,552 10/1958 Evans ....3l3/92 PD X 2,942,129 6/1960 May ..3l3/85 S 3,038,096 6/1962 Knochel et al. ..3l3/85 S FOREIGN PATENTS OR APPLICATIONS 559,316 2/1944 Great Britain..... ..313 92 R Primary Examiner-Robert Segal Att0rney-Clarence R. Patty, Jr., Walter S. Zebrowski and William J. Simmons, Jr.

[57] ABSTRACT A planar member such as a phosphor coated fiber optic plate, having a thermal coefficient of expansion that is incompatible with that of a cathode ray tube envelope and faceplate, is accurately supported a precise distance from the inner surface of the faceplate by a plurality of step-shaped supports having a spacer portion disposed between the planar member and faceplate and a shoulder portion adjacent to the periphery of the planar member. Conductive spring clip means affixed to the supports apply a retaining force to the planar member and make electrical contact thereto.

8 Claims, 4 Drawing Figures I 42 22 so 24 PATENTEDHKY m r will INVENTORS. David R. .Sfeinberg William T. Sutton lllll Ill Fig. 3

Mhjh} ATTORNEY STEPPED SUPPORTS BETWEEN GLASS PLATE DISPLAY SCREEN AND CATIIODE RAY TUBE FACEPLATE BACKGROUND OF THE INVENTION This invention relates to means for mounting a planar member in the path of an electron beam within a cathode ray tube and more particularly to means for accurately mounting a phosphor coated electron beam target with respect to a cathode ray tube faceplate.

It is often desirable to dispose within a cathode ray tube screens, masks, targets or like members, the thermal expansion coefficients of which are not compatible with that of the envelope glass. In some instances it is not advisable to directly seal the member to the envelope or to the faceplate.

One such member, the thermal coefficient of expansion of which is not compatible with that of the tube envelope, is a fiber optic plate. US. Pat. No. 3,335,310 issued Aug. 8, I967 to R. J. Ney discloses a typical example of the manner in which a fiber optic faceplate is sealed to a tube envelope. A thin metal annulus or cylinder is sealed to one end of the tube envelope and a thin metal flange or frame member having a concentric opening therein for receiving the fiber optic faceplate is welded to the metal cylinder. In addition to requiring a plurality of glass to metal seals, the following disadvantages arise from utilizing a fiber optic plate as the faceplate. Fiber optic plates generally exhibit structural weakness, poor heat resistance and poor hermeticity. Moreover, the size and shape of a fiber optic plate may be such as to render it unsuitable for use as a faceplate. For example, some fiber optic plates must be relatively thin in order to provide optimum optical properties and therefore lack sufficient strength to be used as a faceplate.

Supporting means of the type used to support a shadow mask adjacent to a mosaic screen of phosphor dots in a cathode-ray color tube have been considered as a means for supporting a phosphor coated fiber optic plate adjacent to the cathode ray tube faceplate; however, this type of supporting means, which supports the mask from the sidewalls of the tube envelope near the faceplate cannot support the fiber optic plate the required distance from the faceplate with a high degree of accuracy.

In our co-pending application Ser. No. 89,769, now US. Pat. No. 3,660,706 entitled Means for Securing Planar Member to Cathode Ray Tube Faceplate and application Ser. No. 89,715 entitled Improved Means for Securing Planar Member to Cathode Ray Tube Faceplate, both filed on even date herewith, there is disclosed apparatus for accurately mounting a planar member adjacent to the inner surface of a cathode ray tube faceplate. In the first mentioned of said applications, the support apparatus consists of slotted glass posts which are used for supporting a planar member a precise distance from the faceplate. Spring contact means affixed to at least one of the glass posts applies a retaining force to the planar member and makes electrical contact thereto. After first attempting to use large metal posts or clips and encountering difficulties with outgassing of the metal and cracking of the seal between the faceplate and the posts or clips, glass posts were used since glass overcame the problems related to outgassing and to cracking caused by mismatch of thermal coefficients of expansion. However, the glass posts were somewhat difficult to work with and were therefore costly and difficulty was encountered in making electrical contact to the planar member.

In an attempt to provide better electrical contact to the planar member and provide a rugged, easily assembled support apparatus providing more accurate target to faceplate facing, the support apparatus disclosed in the second of said above-identified co-pending applications was developed. That support apparatus comprises support means for disposing a planar member a predetermined distance from the inner surface of a faceplate and a conductive disc having an opening therein situated adjacent to the planar member so that a plurality of fingers which project inwardly from the opening contact the peripheral portion of the planar member. However, the need for improved electrical contact to the target and simpler design and construction lead to the development of the support apparatus of the present invention.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a cathode ray tube having improved means for supporting a member such as a phosphor coated target, mask or the like a precise distance from the inner surface of the faceplate thereof.

Another object of the present invention is to provide improved means for making electrical contact to a member supported within a cathode ray tube.

A further object of the present invention is to provide a simplified, easily constructed apparatus for supporting a planar member within a cathode ray tube.

A'more specific object of the present invention is to provide an improved, simplified apparatus for accurately positioning a photochromic fiber optic plate adjacent to the inner surface of a lens-shaped cathode ray tube faceplate.

Briefly, the cathode ray tube in accordance with the present invention includes an evacuated envelope having means therein for produciiig an electron beam and a faceplate for viewing an optical image produced by the beam. A planar member is disposed a predetermined distance from the inner surface of the faceplate by support means. Spring clamp means are affixed to the support means for applying a retaining force to the member and making electrical contact thereto. Means are provided for applying an electrical potential to the.

spring clip means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in partial cross-section of a cathoderay tube having a planar member secured adjacent to the faceplate in accordance with the present invention.

FIG. 2 is a cross-sectional view taken along lines 2- 2 of FIG. 1.

FIG. 3 is an enlarged, cross-sectional view taken along lines 33 of FIG. 2.

FIG. 4 is a cross-sectional view of a further embodiment of the present invention.

DETAILED DESCRIPTION FIGS. 1 and 2 show a conventional cathode ray tube bulb or envelope comprising the usual constricted neck portion 2, flared portion 4 and end portion 6 against which a lens-shaped faceplate 8 is sealed. An electron source 10, positioned in the constricted portion 2, may comprise conventional means for providing at least one electron beam represented by the dashed line 12. A contact terminal or anode button 18 provides an electrical connection to an internal conductive wall coating 20.

As shown in greater detail in FIG. 3, a planar member such as a phosphor coated target 22 of FIG. 1 is accurately spaced a predetermined distance from faceplate 8 by a plurality of step-shaped supports 24 having a spacer portion 26 disposed between member 22 and faceplate 8 and a shoulder portion 28 adjacent the periphery of target 22. At least two supports are required, and in the disclosed embodiment six supports are used. If the supports are too long, a stress may be induced in the faceplate. Therefore, two narrow supports are used along the longer sides of the target 22 rather than one long support and one narrow support is used along each of the shorter sides. Supports 24 may be made from glass or glass ceramic material, but the preferred material is a metal such as a nickel-copperchrome alloy which has a thermal coefficient of expansion similar to that of the faceplate. Conductive, resilient, U-shaped spring clips 30, 32, 34, 36, 38 and 40 are welded or otherwise secured to that portion of supports 24 remote from the side which contacts faceplate 8.

Since the distance between target 22 and faceplate 8 must be accurately controlled, no bonding material should be located between the supports and the faceplate. The supports are therefore thoroughly cleaned and positioned directly onto the faceplate by a dummy substrate of correct dimensions and expansion coefficient or by some other holding device. Glass solder 42 is then placed around the base of all supports except thatwhich is affixed to spring clip 30 which is left unattached at this time so that the dummy substrate can be replaced by the actual target 22 after these supports are glass soldered to the faceplate. This assembly is placed in a furnace and baked at 440C for 1 hour. The temperature should be increased to 440C at a rate of about lC/min. After the 1-hour bake at 440C, the temperature is decreased to 350C at arate of about 1 HC/min. and thereafterreduced to room temperature at a rate of 6C/min. A solderglass is selected which has a thermal coefficient of expansion that is compati ble with that of the faceplate glass. A lead-zinc-borate glass of the type described in U. S. Pat. No. 2,889,952 issued to S. A. Claypoole may be used.

An enlarged cross-sectional view of a portion of the target 22 is shown in FIG. 3. In this embodiment, the target 22 consists of a photochromic fiber optic plate 43 on which there is deposited a dichroic layer 46, a phosphor layer 48 and an aluminum layer 50. The phosphor layer 48 does not extend to the periphery of the target and a peripheral portion 52 of the aluminum layer is deposited directly on dichroic layer 46. It is not intended that this invention be limited to the target illustrated in FIG. 3. Other targets such as phosphor coated plates of conventional glass, homogenous photochromic glass or conventional fiber optic plates, or other planar members such as screens, masks, or the like could be supported in accordance with the present invention.

After the dummy substrate is removed, target 22 may be inserted into the support assemblies between the spring clips and the spacer portions 26. The spring clips rest on the aluminum coated peripheral portion 52 of the target and provide electrical contact to the target as well as hold it in its proper place. If desired, the remaining support, which is attached to spring clip 30, may be affixed to the faceplate 8 in a manner similar to that by which the other supports were attached. Since the spring clips afflxed to the initially attached supports 24 apply a retaining force to the target, the remaining support may be omitted, especially if the cathode ray tube is to be mounted in such a manner that spring clip 36 is located at the bottom of target 22 during use. A conductive wire 56 can be welded to each of the spring clips either before or after the target 22 is inserted into position. Wire 56 is connected between the anode button 18 and each of the spring clips to provide a good electrical'connection between the anode button 18 and aluminum coating 50. The envelope end portion 6 may now be lowered onto faceplate 8 and glass soldered thereto in a conventional manner.

After the faceplate is sealed to the envelope end portion 6, the entire cathode ray tube is placed in a vacuum system and a layer of conductive material such as aluminum is evaporated onto flared portion 4, end portion 6, target 22 and that part of' faceplate 8 that is not in the shadow of the target. This can be accomplished by inserting the evaporation source into the neck portion 2. For the sake of clarity the only conductive layer illustrated as resulting from this process is layer 62 on faceplate 8, since the envelope walls and the target were previously coated with conductive material. Aluminum layer 62 provides a reflecting surface on that part of the faceplate not occupied by target 22. This reflecting surface aids in bleaching photochromic glass in the target 22. The aluminum layer also insures good electrical contact between the anode pin 18 and the conductive coating 20.

The connection between anode button 18 and the spring clips could be made by conductive coatings 20 and 62, thereby eliminating the need for wire 56. In this modified embodiment, supports 24 must be made from a conductive material. Care must be taken'to make a good connection between coatings 20 and 62 since their junction occurs at the junction of the faceplate and the tube end portion 6.

In the embodiment shown in FIG. 4, elements similar to those of FIGS. 1-3 are indicated by primed reference numerals. In this embodiment, that portion of wire 56 extending from clip 30 to the anode button is replaced by one or more modified clips which are mounted on a support 24 but which have a contact arm that contacts conductive coating 20' as well as contacting the peripheral portion of target 22'. The wire 56' makes an electrical connection between modified clip 70 and the remaining clips of the type shown in FIGS. 1-3.

The fiber optic plate 43 of FIG. 3 is made up of many very fine individual fibers 44 which are joined by fusion in side-by-side relation with each other, the ends of these fibers forming two planar surfaces of the plate 43.

Each of the fibers 44 consists of a core of a light transmitting medium having a relatively high index of refraction surrounded by a relatively thin cladding of glass having a relatively low index of refraction. The cores of the fibers are made from photochromic glass, which has the property of becoming less transparent when irradiated with blue or ultraviolet light, remaining unaffected by green light and becoming more transparent when irradiated by infrared, red or orange light. The characteristics and production of such glass are described in U. S. Pat. No. 3,208,860 granted to W. H. Armistead and S. D. Stookey on Sept. 28, 1965. The cladding glass may consist of that which is taught in U. S. Pat. No. 2,382,056 granted to H. P. Hood on Aug. 14, 1945.

The dichroic layer 46 transmits ultraviolet light having a wavelength around 350 nm and reflects light having a wavelength above 450 nm. The layer 46 is typically multilayered and may be formed by well-known evaporating techniques. Phosphor layer 48 is selected for the wavelength of light which it radiates when excited by the electron beam. The light radiated by the phosphor is preferably ultraviolet light which passes through dichroic layer 46 and darkens those photochromic fibers 44 on which it impinges. Selected portions of the photochromic fiber optic plate 43 may be darkened by controlling the position and intensity of the electron beam to write and store information therein.

Referring to FIGS. 1 and 3 information stored in the target 22 is read therefrom by directing onto faceplate 8 a beam of green light represented by the arrows 76. This probing light is focused by the lens-shaped faceplate onto fibers 44, passes through the fibers, reflects from dichroic layer 46 and again passes through fibers 44. The resultant image may be projected by a lens system which includes faceplate 8. Mounting the target 22 to the faceplate 16 in the manner disclosed herein provides the accurate positioning that is necessary to insure that the target is properly centered with respect to the faceplate and properly spaced therefrom, thus permitting the accurate positioning of the target in the optical system.

We claim:

l. A cathode ray tube comprising an evacuated envelope,

means in said envelope for producing an electron beam,

a faceplate forming a part of said envelope,

a glass plate disposed adjacent the inner surface of said faceplate,

a layer of phosphor disposed on that surface of said glass plate which is remote from said faceplate, said phosphor layer being so disposed in said envelope that it is adapted to receive electrons from said electron beam producing means,

a conductive layer disposed upon the surface of said phosphor layer,

a plurality of support means affixed to said faceplate means for applying a retaining force to said member and making electrical contact thereto,

said support means and said spring clip means providing the sole support for said glass plate, said spring clip means comprising a resilient, U-shaped clip having one end affixed to a corresponding step-shaped support and a second end disposed against a peripheral portion of said glass plate in contact with said conductive layer, and means for applying an electrical potential to said spring clip means comprising a terminal disposed on the inner surface of said envelope.

2. A cathode-ray tube in accordance with claim 1 which further comprises a conductive wire electrically connecting said terminal to said U-shaped clips.

3. A cathode-ray tube in accordance with claim 1 wherein said step-shaped supports are conductive, and further comprising a first conductive coating disposed on a portion of the inner surface of said envelope in contact with said terminal and a second conductive coating disposed on a portion of said faceplate between said first conductive coating and said step-shaped sup-- ports.

4. A cathode-ray tube in accordance with claim 1 further comprising a conductive coating disposed on a portion of the inner surface of said envelope in contact with said terminal, at least one of said U-shaped clips including a resilient contact arm extending to said conductive coating.

5. A cathode-ray tube in accordance with claim 4 further comprising a conductive wire electrically connecting said at least one U-shaped clip to the remaining ones of said U-shaped clips.

6. A cathode-ray tube in accordance with claim 1 wherein said faceplate is lens-shaped.

7. A cathode-ray tube in accordance with claim 6 wherein said glass plate is a fiber optic plate. 7

8. A cathode-ray tube in accordance with claim 7 wherein said fiber optic plate comprises a plurality of fibers in side-by-side relation with each other, the ends of said fibers forming two planar surfaces, each fiber consisting of a core of photochromic glass having a given index of refraction surrounded by a cladding of glass having an index of refraction lower than that of said core. 

1. A cathode ray tube comprising an evacuated envelope, means in said envelope for producing an electron beam, a faceplate forming a part of said envelope, a glass plate disposed adjacent the inner surface of said faceplate, a layer of phosphor disposed on that surface of said glass plate which is remote from said faceplate, said phosphor layer being so disposed in said envelope that it is adapted to receive electrons from said electron beam producing means, a conductive layer disposed upon the surface of said phosphor layer, a plurality of support means affixed to said faceplate and spaced around the periphery of said glass plate for disposing said glass plate a predetermined distance from said faceplate, said support means comprising a plurality of step-shaped supports having a spacer portion disposed between said glass plate and said faceplate and a shoulder portion disposed adjacent the peripheral portion of said glass plate, spring clip means affixed directly to said support means for applying a retaining force to said member and making electrical contact thereto, said support means and said spring clip means providing the sole support for said glass plate, said spring clip means comprising a resilient, U-shaped clip having one end affixed to a corresponding step-shaped support and a second end disposed against a peripheral portion of said glass plate in contact with said conductive layer, and means for applying an electrical potential to said spring clip means comprising a terminal disposed on the inner surface of said envelope.
 2. A cathode-ray tube in accordance with claim 1 which further comprises a conductive wire electrically connecting said terminal to said U-shaped clips.
 3. A cathode-ray tube in accordance with claim 1 wherein said step-shaped supports are conductive, and further comprising a first conductive coating disposed on a portion of the inner surface of said envelope in contact with said terminal and a second conductive coating disposed on a portion of said faceplate between said first conductive coating and said step-shaped supports.
 4. A cathode-ray tube in accordance with claim 1 further comprising a conductive coating disposed on a portion of the inner surface of said envelope in contact with said terminal, at least one of said U-shaped clips including a resilient contact arm extending to said conductive coating.
 5. A cathode-ray tube in accordance with claim 4 further comprising a conductive wire electrically connecting said at least one U-shaped clip to the remaining ones of said U-shaped clips.
 6. A cathode-ray tube in accordance with claim 1 wherein said faceplate is lens-shaped.
 7. A cathode-ray tube in accordance with claim 6 wherein said glass plate is a fiber optic plate.
 8. A cathode-ray tube in accordance with claim 7 wherein said fiber optic plate comprises a plurality of fibers in side-by-side relation with each other, the ends of said fibers forming two planar surfaces, each fiber consisting of a core of photochromic glass having a given index of refraction surrounded by a cladding of glass having an index of refraction lower than that of said core. 